The present invention relates to AC-DC power distribution systems, and in particular to power distribution systems that include DC content protection.
AC-DC power distribution systems are employed in a variety of applications to distribute power from an AC generator to a plurality of connected loads. For example, in aerospace applications a variable frequency AC generator distributes AC power to a plurality of loads (either AC or DC loads). In a typical system, a few centralized transformer based rectifier units (TRUs) are used to convert AC power to DC power for distribution to a plurality of DC loads. The TRUs remain isolated from one another and provide little if any DC content as a result of failures (e.g., diode failures).
There has been a trend in aerospace applications (as well as in other fields) for more electronic loads that individually rectify the AC power to a high-voltage DC level. Passive or active rectification, such as that provided by autotransformers, is susceptible to faults (e.g., diode faults, DC link faults, etc.) that place DC content onto the AC distribution system. Without the electrical isolation provided by TRUs employing a two-winding transformer, DC content generated as a result of a fault at one load is propagated to other loads connected to the AC distribution system. That is, because each of the plurality of loads is connected in common with the AC generator, the DC content provided by a faulty load can be communicated to other loads on the distribution system, resulting in the potential damage, overheating, or inefficiency of the loads. In addition, DC content may be propagated to the AC generator. Significant DC content (e.g., DC currents) on the stator coils of the generator may result in the generator becoming saturated, and ultimately lost (i.e., shut-down).
It would be beneficial to provide an AC-DC power distribution system that isolates faulty loads contributing DC content to the AC distribution system and prevents the DC content from tripping the AC generator or damaging other loads connected to the AC generator.